In recent electronic devices, a high-featured electronic circuit is often built therein which includes a large number of functional blocks, such as a processor, a DSP (digital signal processor), and dedicated hardware, each of which has a particular processing function. The electronic circuit including the large number of functional blocks is integrated into a semiconductor integrated circuit such as an IC or an LSI in order to meet the requirement for downsized electronic devices. With the integration of the electronic circuit into the semiconductor integrated circuit, super-fine processes such as 90-nm and 65-nm rules are now applied to the semiconductor integrated circuit.
However, super-fine processes involve large leakage current from each transistor unit, and result in increased leakage current from the semiconductor integrated circuit when the semiconductor integrated circuit is both deactivated and operated. In addition, the highly integrated semiconductor integrated circuit brings about a large total leakage current.
Accordingly, the leakage current must be reduced to provide reduced power consumption in an electronic device having the semiconductor integrated circuits incorporated therein.
In particular, with battery-driven handheld terminals, the increased leakage current results in a decreased period of time for which the handheld terminals are operable, and therefore a reduction in the leakage current is important.
In a typical electronic device, the electronic circuit and semiconductor integrated circuit disposed therein are supplied with electrical power together with the power source of the electronic device. The electrical power continues to be supplied to the electronic circuit and semiconductor integrated circuit, even when these circuits need not be operated. This causes a problem in which unwanted electrical power is consumed, regardless of an actual quantity of operation.
To avoid the problem, an art operable to provide a controlled supply of electrical power has been proposed.
According to an art disclosed by cited Reference No. 1 (published Japanese Patent Application Laid-Open No. (HEI) 7-141074), an external control interrupts the supply of power to functional blocks mounted in a semiconductor integrated circuit, in which each of the functional blocks has a particular processing function.
FIG. 16 is a block diagram illustrating an electronic circuit as disclosed by cited Reference No. 1.
The electronic circuit 700 includes a first functional block “703a” through an eighth functional block “703h”, each of which has a particular processing function. Each of the first through eighth functional blocks “703a”-“703h” is a block having a different specific processing function such as image processing, voice processing, and memory access. A power supply control unit 701 has control of the supply and shutoff of power to the first through eighth functional blocks “703a”-“703h”. A power control register 702 is operable to store externally written data on power control. The power supply control unit 701 is operable to control the supply and shutoff of power to the first through eighth functional blocks “703a”-“703h” in accordance with the power control data stored in the power control register 702.
The power control data is written to the power control register 702 through an exterior processor. This system allows external settings to control the supply of power to each of the plurality of functional blocks.
According to an art disclosed by cited Reference No. 2 (published Japanese Patent Application Laid-Open No. 2002-341976), the power supply is controlled in accordance with a stop mode signal from a processor built in a semiconductor integrated circuit.
FIG. 17 is a block diagram illustrating a system LSI as disclosed in cited Reference No. 2.
The system LSI 800 includes a CPU 803, a circuit “A” 804, and a circuit “B” 805. The CPU 803 sends out the stop mode signal to a control circuit 807 when each of the circuit “A” 804 and the circuit “B” completes a course of action. The control circuit 807 stores an externally outgoing signal in a backup register 808 upon receipt of the stop mode signal, and then sends out a shutoff-requesting signal to a power source 801. The power source 801 receives the shutoff-requesting signal and interrupts the supply of the power to the system LSI 800.
According to the power supply control as just discussed above, the termination of a course of action provided by each functional block integrated in a semiconductor integrated circuit is detected, whereby the controlled supply of power to each of the functional blocks is attainable.
However, a problem with the prior art power supply control is that heavy loads are imposed on the monitoring and processing required of the power supply control. In addition, the power supply control cannot be practiced within fine limits.